Foliar feeding of boron influencing biochemical attributes and enzyme activity in dragon fruit (Selenicereus monacanthus)

Boron plays crucial role in metabolic processes during fruit ripening and in turn ensures better fruit quality. However limited studies have been conducted to assess the influence of boron on fruit quality of dragon fruit. In the present study, the efficacy of boron was investigated on red-fleshed dragon fruit (Selenicereus monacanthus). Four levels of boron (100 mgL-1, 200 mgL-1, 300 mgL-1 and 400 mgL-1) were applied on 7- and 14-day-old flower buds. The highest pollen germinability, seed weight, fruit weight (274.32 ± 36.72g), pulp content (70.80 ± 1.79%) and pulp firmness (2.74 ± 0.18 N) were recorded when B was applied@300 mg L-1 on 7-day old flower bud. The same treatment also manifested higher soluble solid contents (17.42 ± 0.62 °Brix), sugar content, total carbohydrate (15.92 ± 1.12%), protein (1.33±0.11%), ascorbic acid (112.66 ± 4.98 µg/g), betacyanin (32.86±2.52 µg/g), total phenol (95.26 ± 3.72 µg GAE/ 100g), total flavonoid (37.65 ±2.14 mg QE/100g) and anti-oxidative activity (27.71±2.14 mM Fe II/100g). Correlation studies elucidated significant positive influence of pollen germinability on fruit weight, pulp content and pulp firmness. The activities of α-amylase, invertase and sucrose synthase enzymes were significantly upregulated with the application of B 300 mg L-1 on 7-day old flower bud. On the other hand, the activities of cell wall degrading enzymes such as cellulase, polygalacturonase and pectin methyl esterase were reduced with increasing levels of boron. The principal component analysis (PCA) illustrated the maximal proximity of most of the quality attributes with B 300 mgL-1, applied at 7-day old flower bud stage, thus exemplifying it as the best treatment.